6 Weird Things Your Fitbit Knows About Your Health

Chances are you have at least one friend, coworker, or cousin—or maybe it's you?—who's obsessed with her Fitbit and reaching that coveted 10,000-step mark every day. But tracking your steps isn't all it's good for. Useful as they are in helping people get active, these wearable devices can potentially clue you in to way more about your health than your walking habits. (Get a flat belly in just 10 minutes a day with our reader-tested exercise plan!)

Because these monitors track your heart rate, they can potentially alert you to everything from pregnancy to scarier stuff, like heart problems. While a Fitbit isn't meant to be used as a medical device, the stories below prove that, as Mitesh Patel, MD, an assistant professor of medicine at the University of Pennsylvania, says, "there's potential to use them in a clinical setting." In fact, doctors at Duke are already using mobile technology to help patients remotely relay blood pressure information to their doctors. Ricky Bloomfield, MD, director of mobile technology strategy at Duke University School of Medicine, says that he's excited for when medical information like blood pressure, weight, activity level, and heart rate are easy to measure—and measure constantly. "Consumers have these wearable devices, and they want to use them to benefit their health," he says. "Now it's up to us in the health system to make that happen."

Below, six stories of people who already did. While the science is stronger in some of these cases than others, one thing is certain: There's a lot of potential literally at your fingertips.

1. That you're pregnant

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The story: Although a Fitbit isn't likely to replace the good old-fashioned pregnancy test, the device has proved its ability to predict that at least one woman is expecting. According to this story, a man noticed some unusual data on his wife's Fitbit: She'd logged 10 hours in the "fat-burning" zone, meaning her heart rate had been 110 beats per minute or higher. Numbers like that should have been impossible given her activity level—most people's resting heart rate is in the 70s—so he took to a Reddit discussion board to ask other Fitbit users what was going on. One user asked if she might be pregnant and, it turns out, she was.

A doctor says: While it's possible that the device was malfunctioning and she just happened to be pregnant, there's a good chance this woman's Fitbit really did clue her in to her pregnancy. "During pregnancy, a higher heart rate is a normal physiological response," says Aaron Aday, a cardiology fellow at Brigham and Women's Hospital. "The heart beats faster because there's additional blood pumping through your body and new metabolic demands to provide blood, oxygen, and nutrients to the developing fetus."

2. That your heart isn't working right

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The story: You may have heard about the 42-year-old man whose doctors credit his Fitbit with saving his life. If not, here's the gist: A man arrived at the ER to get treatment for a seizure, and after doctors checked his Fitbit data, they realized that his heart rate had been extremely high—between 140 and 160 beats per minute—3 hours before he arrived. With this information, the doctors deduced that the man had had an atrial fibrillation hours before the seizure, which helped them decide to use electric shock to drop his heart rate back to a normal level.

A doctor says: It's possible that the Fitbit saved this man's life, but probably not, says Aday. "There certainly can be interplay between the heart and brain," he says. But doctors most likely would have been able to treat him even without the heart rate data from his fitness tracker.

3. That your blood isn't flowing properly

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The story: Plagued with extreme fatigue after getting her tonsils removed, one woman says she would've just attributed her lack of energy to the surgery had it not been for her Fitbit, she wrote on a Fitbit discussion board. It was only because her activity tracker was showing a super-high heart rate that she decided to visit her doctor, who quickly discovered she had blood clots in her lungs.

A doctor says: Her fast heart rate could definitely have clued her in to her clots, says Aday. Most blood clots start in your legs, then break off and travel through your circulatory system, passing through the right part of your heart and eventually lodging in your lungs. "When that happens, it's a little like a blocked pipe, and to compensate for that, the heart beats faster," Aday says.

The story:Fitbit discussion boards also tell the tale of a man who got a brand-new Fitbit in the mail, tried it on, and thought it was faulty because the heart monitor read 98 beats per minute, which is on the higher side of normal. When he had a friend test it out and saw the heart rate read 72, the man decided to head to the doctor. He soon had a diagnosis of myocarditis—an inflammation in the heart that, left untreated, could cause permanent damage.

A doctor says: While the Fitbit might have been picking up on this man's heart inflammation, it's unlikely that it was the first sign that something was going on. "Most people who have myocarditis aren't coming in for heart rate issues," Aday says. Usually, they first notice other symptoms like chest pain, trouble breathing, palpitations, lightheadedness, fever, or chills.

5. That you're heartbroken

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The story: Ever wonder how your heart actually reacts during a breakup? Now we know, thanks to a tweet from one Fitbit user who had just gone through a breakup. After spending the day in a funk, he turned on his Fitbit later that night and made an interesting discovery. The moment his now ex-boyfriend called—around 12:30 PM—the man's heart rate jumped from a resting 72 to 88, and then continued to climb throughout the day before peaking at 118. (Here are 10 little things connected couples do.)

A doctor says: Yes, a Fitbit really can track your emotional ups and downs. "We've known for decades that stressful experiences can cause a jump in heart rate," Aday says. Just think about when your heart pounds before you have to give a public speech or approach your boss to ask for a raise. The moments leading up to and right after a stressful experience like that would likely cause the same kind of spike as this breakup.

The story: This Fitbit moment is a favorite of Daniel Shaw's, product-marketing manager for the company: According to company lore, there was a man whose Fitbit always showed a slightly high resting heart rate. But that all changed when he broke up with his live-in girlfriend. Soon after she had packed up her stuff and left, his heart started to slow down and found a new, less-stressed resting place.

A doctor says: Again, the heart monitor on Fitbit trackers can measure emotional stress. Yet, Aday says, it'd be harder to track in this case. "It's hard to maintain the same level of stress at all times," he says. Unless the man was constantly stressed while his girlfriend lived with him, it's unlikely that his resting heart rate would be high only because of her.

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